Fluid metering apparatus having drip prevention means



April 19, 1966 E. w. LIDELL ETAL 3,246,808

FLUID METERING APPARATUS HAVING DRIP PREVENTION MEANS Filed May 18, 19642 Sheets-Sheet l INVENTORS EDWIN W. LIDELL GEORGE J. BURSAK ATTORNEYApril 19, 1966 E. W. LIDELL ETAL FLUID METERING APPARATUS HAVING DRIPPREVENTION MEANS Filed May 18, 1964 ii 18 i I? 2 Sheets-Sheet 2 HWW W\NVENTORS EDWIN W. LlDELL.

GEORGE J. BURSAK ATTORNEY United States Patent FLUID METERING APPARATUSHAVING DRIP PREVENTION MEANS Edwin W. Lidell, Brookiieid, and George J.Bursak, Milwaukee, Wis., assignors to Bursak Packaging Machinery Corp,Jackson, Wis., a corporation of Wisconsin Filed May 18, 1964, Ser. No.368,127 8 Claims. (Cl. 222-330) This invention relates to a fluidmetering apparatus, and more particularly resides in an apparatus forcontrolling the feeding of a selected volume of a fluid from a sourceand through distribution means, which apparatus includes means forpositively halting the flow of fluid to the distribution means oncethe'selected volume has been discharged through the distribution meansand for thereafter insuring that fluid accumulated in the distributionmeans will not be discharged.

In numerous modern applications it is necessary to deliver upondemandfixed, preselected volumes of a material for processing. Onegeneral area in which such 'a requirement exists is the field offlexible packaging wherein it is often desirable to introduce fluidmaterials (and by this is generally. meant liquids and liquids withsuspended solids) to be packaged into the flexible packages as they arebeing formed. In many instances the volume, or the Weight which can berelated to the volume, must be controlled to a greater degree ofprecision. Examples are thepackaging of foodstuffs which require aweight designation and the packaging of paint pigments adapted foraddition to neutral bases to yield a desired color. Obviously, in thepackaging of foodstuffs, supplying a lesser or a greater volume of fluidmaterial will result in misbranding or economic lossto the processor,and that in the instance of the paint pigment additives the accuracy ofthe volume supplied will control the trueness of the resultant paintcolor.

In general, a system for feeding the fluid material to a dispensingpoint would include a pump to deliver the fluid under pressure from asource, distribution means generally including conduits leading to thedispensing point, and controllable valve means connected in the systembetween the source and dispensing point and which'functions to controlthe delivery of the selected volumes of the fluid to the dispensingp'oint. Unless the valve means is disposed at the precise end of thedistribution means, which is generally impracticable because ofinterference with processing equipment to which the fluid is to bedelivered, there is always some material in the conduits of thedistribution means beyond the valve means after the selected volume hasbeen dispensed and the flow halted. There is considerable danger of thefluid material in the conduits being accidentally discharged from theend of the conduits thereby upsetting the metered volume. The accidentaldischarge may result from the pressure of the fluid in the conduits or,in the case of a gravity feed, from the weight of the fluid.

The apparatus of this invention prevents the false delivery of excessivequantities of fluid material by including valve means actuable topositively block the flow of the fluid from the source once the selectedvolume has been dispensed and which further includes means which createa partial vacuum once the flow of fluid has been blocked 1 a fluidmetering apparatus which positively and accurately controls the deliveryof selected volumes of a fluid to a dispensing point.

It is another object of this invention to provide a fluid meteringapparatus which halts the flow of the fluid once a selected volume hasbeen dispensed and which thereafter will suck back the fluid indistributing conduits beyond the apparatus to prevent accidentaldischarge of excess quantities of the fluid from the conduits.

It is a further object of this invention to provide such a fluidmetering apparatus including a controllable valve which in its openposition permits fluid to flow from a source to a delivery conduit andwhich when closed halts the flow and creates a partial vacuum to draw aportion of the fluid in the delivery conduit back to the apparatus toprevent discharge of excess quantities of the fluid.

It is also an object of this invention to provide such a fluid meteringapparatus including simple adjustment means to permit selection of theamount of suck-back created to accommodate fluids of various viscositiesand distribution systems of varied capacities and characteristics.

It is a further object of this invention to provide a fluid meteringapparatus including a plurality of valve assemblies each connectablebetween a source of the fluid and a dispensing point to control thedelivery of fluid to the dispensing points, together with actuable meansto simultaneously close each of the valve assemblies to halt the flow offluid and to suck back fluid to the assemblies.

The foregoing and other objects will appear in the description tofollow. In the description, reference is made to the accompanyingdrawings which for-m a part hereof and in which there is shown by way ofillustration specific embodiments in which this invention may bepracticed. The embodiments will be described in 'suflicient detail toenable those skilled in the art to practice this invention, but it is tobe understood that other embodiments of the invention may be used andthat structural changes may be made in the embodiments described withoutdeparting from the scope of the invention. Consequently, the followingdetailed description is not to be taken in a limiting sense; instead,the scope of the present invention is best defined by the appendedclaims.

In the drawings:

FIG. 1 is a view in elevation of a fluid feed system including the fluidmetering apparatus of the present invention;

FIG. 2 is atop plan view of the fluid metering apparatus of FIG. 1; i

FIG. 3 is a view in vertical section taken of the line 33 of FIG. 2;

FIG. 4 is a view in vertical section similar to that of FIG. 3 butillustrating the apparatus in a closed position;

FIG. 5 is a view in vertical section through a second embodiment of aplunger assembly of the apparatus; and

FIG. 6 is a view in vertical section similar to FIG. 5 but showing theplunger assembly in a closed position.

Referring to the drawings, a pump 10 delivers a fluid to be dispensedfrom a source 11'to an inlet conduit in the form of a hollow conicalmember 12 which has a greater cross sectional area at its top than atits bottom. A can plate 13 seats with the upper peripheral edge of theconical member 12 and is secured thereto by a hexagonal nut 14. The nut14 has a radially inward extending flange 15 which engages a ledge 16 onthe cap plate 13, and the nut 14 is threadedly engaged about the upperend of the conical member 12.

The cap plate 13 supports the fluid metering apparatus which broadlycomprises a plurality of plunger assemblies 17, four in number in theembodiment shown, and actuating means in the form of an air cylinderassembly 18 employed to control the opening and closing of the plungerassemblies 17. Specifically, the four plunger assemblies 17 are arrayedabout the central air cylinder assembly 18 at equally spaced intervals.The cap plate 13 has four equally spaced through bores 19 each of in theplane which receives a reduced lower end portion 21) of a hollow plungercylinder 21. The reduced end portion of each 2 cylinder 21 is journaledin a respective through bore 159 to have a lower inlet opening 22 to thehollow interior of the plunger body communicate with the hollow interiorof the conical member 12.

K Each inlet opening 22 leads to an inlet passage 23 in the plungercylinder 21 and which in turn leads to a central chamber 24. A threadedoutlet opening 25 extends transversely into the central chamber 24 ofthe plunger cylinder 21 and a needle valve 26 is 'threadedly received inthe outlet opening 25. The needle valves 26 may be of known constructionand are adopted to be connected to supply conduits (not shown) whichlead to the ultimate dispensing points for the fluid.

The plunger cylinder 21 is provided with an enlarged upper bore 27 abovethe central chamber 24 and which is of a larger diameter than that ofthe inlet passage 23, for reasons which will appear hereafter. Apistonin the form of a plunger guide 28 is slideably received within theupper bore 27 of each plunger cylinder 21 and is sealed with theinterior of the upper bore 27 by a pair of O-rings 29 supported inannular recesses in the plunger guide 28. The plunger guide 28 has acentral bore 30 which receives a plunger rod 31 that is threaded at itsupper end and engaged in an internally threaded upper enlarged portion32 of the guide 28. The plunger rod 31 projects downwardly through thecentral chamber 24 and the inlet passage 23 to terminate in a plunger33. The plunger rod 31 is sealed with the central bore 30 of the guide28 by an O-ring 34.

The plunger 33 is disposed within the hollow interior of the conicalmember 12 when the plunger assembly 17 is open. The outside diameter ofthe plunger 33 is slightly less than. that of the inlet passage 23 andthe plunger 33 is adapted to be retracted within the inlet passage 23when the plunger assembly 17 closes. An O-ring 35 is mounted in anannular recess 36 in the outer periphery of the plunger 33 to wipe thewalls of the inlet passage 23 as the plunger .33 is retracted.- Y

The upper enlarged portion of the plunger guide 28 seats upon the upperend of the plunger cylinder 21 when the plunger assembly 17 is in afully open position. The position of the plunger 33 when the plungerguide 28 is in its lowermost open position may be varied by means of thethreaded engagement of the rod 31 and the guide 28. Once the properposition has been determined the rod 31 is retained by a jam nut 37which surrounds the threaded end of the plunger rod 31 and rests againstthe upper end of the plunger guide 28.

The air cylinder assembly 18 comprises an air cylinder 38 having aprojecting stud 39 at its bottom which is threadedly engaged in a tappedhole 40 provided in 'the centerof the cap plate 13. A piston 41 operatesin the air cylinder 38 and has its piston rod '42 extending upwardly andprojecting through the cylinder 38. Upper and lower air ports 43 and 44,respectively, are provided in the cylinder 38 and are adapted to admitair under pressure either above or below the piston 41, as desired.

The extending upper portion of the piston rod 42 is threaded to receivea cover plate 45. The cover plate 45 has four equally spaced notches 46in its outer periphery and each notch is adapted to engage an annularrecess 47 provided in the enlarged portion 32 of each plunger guide 28.The vertical position of the cover plate 45 on the piston rod 42 may bevaried and once selected may be retained by a jam nut 48.

In operation, the fluid to be dispensed is pumped by the pump 10 fromthe source 11 to fill the conical member 12. With the piston 41 in itslowest position, the plunger assemblies 17 are open with the elementsassuming the positions shown in FIG. 3. The plunger guides 28are intheir lowest position with the enlarged upper portions 32 resting uponthe cylinders 21. The plungers 33 are disposed in the fluid filling theconical member 12. The

fluid under pressure in the conical member 12 is then free to passthrough the inlet openings 22 and along the inlet passages 23 andcentral chambers 24 to the outlet openings 25 to enter the needle valve26 and pass thence to the point of distribution. When a desiredpreselected quantity of the fluid has passed through each outlet opening25, the air cylinder assembly 18 is actuated by admitting air underpressure through the lower air port 44 thereby causing the piston 41 andpiston rod 42 to move suddenly upwardly. The upward movement of thepiston 41 and piston rod 42 carries with it the four plunger guides 28.As the plunger guides 28 are moved upwardly each of the plungers 33 areretracted into their respective inlet passage 23 to halt the flow offluid to the needle valve 26.

This action 'would be suificient to stop the dispensing of the fluidexcept that the inlet passages 23, the central chambers 24, the needlevalves 26 and the ultimate distribution lines will be full of fluidwhich can find its way to the dispensing points and be unintentionallydischarged either because of the pressure of the accumulated fluid or bythe effects of gravity. To prevent this, the apparatus of this inventioncreates a partial vacuum in the cylinders 21 to result in a pressurediflerential which will draw fluid back into the cylinders 21 from theneedle valve 26 and the distribution lines connected thereto. Thisoccurs by the withdrawal of the plunger guides 28 within the upper bores27 of the cylinders 21. Since the volume vacated as each plunger guide28 withdraws is greater than the volume displaced by the upward movementof a plunger 33 through the inlet passage 23, a suck-back is created toprevent the accidental discharge of the accumulated fluid which woulddestroy the accuracy of the metered volume. The closed position of theplunger assemblies 17 is shown in FIG. 4.

When it is again desired to dispense the selected volume of the fluid,the air beneath the piston 41 is evacuated from thecylinder 38 throughthe lower a-ir port 44 and air under pressure is admitted through theupper air port 43. The piston 41 and its piston rod'42 will be moveddownwardly to open all of the plunger assemblies 17 and permit the flowof fluid to the dispensing points to begin anew.

' The pump 10 may be employed to maintain a continuous supply of thefluid to the conical member 12 so that the pressure of the fluid at thetop of the conical member 12 is constant. The air cylinder assembly 18is then used to exclusively control the volume of the dispensed fluid byopening and closing the plunger assemblies 17. Alternately, 'both' thepump 10 and the air cylinder assembly 18 may be used in unison todispense the selected volume. That is, once the conical member 12hasbeen filled with the fluid the air cylinder assembly 18 can be actuatedto open the plunger assemblies '17 and at thesame time the pump 10 canbe'driven to begin feeding the fluid through the outlet openings 25. Theplunger assemblies 17 then remain open until the selected volume hasbeen fed bythe pump 10 at which time the pump 10 is stopped and the aircylinder assembly 18 is actuated to close the plunger assemblies 17.

By varying the position of the cover plate 45 on the piston rod 42 andby varying the position of the plunger rods 31 in the guides 28,adjustment of the amount of "travel in the withdrawal stroke of theguides 28 may be achieved and the extent of the suck-back may be varied.In such manner, the apparatus may be adjusted to accommodate fluidshaving diflerent characteristics of flow and ultimately distributionsystems of various configurations. Generally, fluids of low viscosityrequire a short travel of the guide 28 and fluids of larger viscosityand particularly those which include suspended solids require a largertravel to produce the necessary amount of suckback.

Referring now to FIGS. Sand 6, there is shown therein an alternateembodiment of a plunger assembly for use in the apparatus of thisinvention. Specifically, a plunger rod49 is slideably received in thecentral through bore 50 of a plunger guide 51 similar to the guides 28,and extends through the plunger guide 51 to terminate at its upper endin a threaded portion that mounts a washer 52. A compression spring 53is biased between the washer 52 and the upper end of each plunger guide51. An O-ring 54 is mounted about the plunger rod 49 to work within thecentral bore 50 of the plunger guide 51. Each plunger rod 49 is alsoprovided with an upset annular shoulder 55 which normally seats againstthe lower end of the plunger guide 51 under the urging of thecompression spring 53.

The lower end of the plunger rod 49 terminates in a plunger 56 having aresilient valve seat 57 mounted thereon and adapted to seat upon theinlet opening 22 of the plunger cylinder 21 to close the entrance to theinlet passage 23. An O-ring 58 is supported about the plunger 56 to workin the inlet passage 23.

The operation of the embodiment of FIGS. 5 and 6 is similar in mostrespects to that of the embodiment of FIGS. 1-4. However, the actuationof the air cylinder assembly 18 to close the plunger assemblies 17 willcause the plunger guides 51 and rods 49 to move upwardly in unison untileach valve seat element 56 closes with its respective inlet opening 22.Further upward movement of the piston 41 will carry the plunger guides51 upwardly independently of the rods 49 and the volume vacated by thecontinued withdrawal of the guides 51 will result in the desiredsuck-back action. The open and closed positions of the alternate plungerassembly are shown in FIGS. 5 and 6, respectively.

Again, by varying the position of the cover plate 45 on the piston rod42, the amount of the suck-back can be adjusted for best results in theenvironment for the fluid being dispensed.

Throughout, the term fluids has been employed to describe the type ofmaterial upon which the apparatus of this invention is operative. It isnot intended by the use of this term to limit the range of applicabilityof the apparatus. Fluids can encompass liquids and liquids withsuspended solids, both minute and substantial, and other forms ofmaterial whichare capable of being fed through the apparatus and areresponsive to the suck-back action produced.

Any suitable actuating means such as a hydraulic cylinder or a solenoidmay be used in place of the air cylinder assembly 18. Likewise, any formof pump including a reciprocating piston may be employed to initiallyfeed the fluid to the hollow conical member 12; or a gravity feed to themember 12 may be used.

It will be seen from the foregoing description that an apparatus inaccordance with this invention provides a simple yet eflicient means forpositively controlling the dispensing of selected volumes of fluids withaccuracy. While the invention is useful for controlling the dispensingof a fluid generally, it can be particularly advantageously employed fordispensing fluids to flexible packages, blister packages, and rigidcontainers. When used in connection with flexible or blister packagingthe suck-back action will prevent any dripping of the fluid which couldcontaminate the seals of the packages and destroy their effectiveness.

We claim:

1. In an apparatus for controlling the dispensing of a selected volumeof a fluid from a source of the fluid under pressure to a point ofdistribution of the fluid, the combination comprising: a hollow cylinderhaving an inlet communicating with said source, an outlet communicatingwith said point of distribution, a first passage connecting said inletand said outlet, and a second passage communicating with said firstpassage beyond said inlet and of a greater cross section than said firstpassage; plunger means movable in said first passage between an openposition in which said inlet is open for the passage of fluidtherethrough and a closed position in which said plunger means obstructssaid first passage to halt the flow of fluid to said outlet; pistonmeans movable in said second passage and adapted when withdrawn tovacate a volume in said cylinder greater than that displaced by movementof said plunger means to said closed position whereby a partial vacuumis created to draw fluid into said cylinder through said outlet; andactuating means adapted when actuated to move said plunger means to saidclosed position and to withdraw said piston means, whereby thedispensing of fluid in excess of said selected volume is prevented.

2. In an apparatus for controlling the dispensing of a fluid from aninput conduit connected to a source of the fluid to an output conduitconnected to a point of distribution of the fluid, the combinationcomprising: a cylinder having an open inlet end communicating with saidinput conduit, an outlet communicating with said output conduit, and afirst passage connecting said inlet and said outlet; plunger meansmovable between an open position in which said inlet isopen for thepassage of the fluid therethrough and a closed position in which saidplunger means obstructs said first passage to prevent further flow ofthe fluid to said outlet; vacuum means including a second passage insaid cylinder means communicating with said outlet and piston meansmovable in said second passage and operable upon said plunger means tomove the same; and actuating means adapted when actuated to move saidpiston means to move said plunger means to said closed position and toretract said piston means within said second passage to create a vacuumwithin said cylinder to draw fluid into said cylinder through saidoutlet.

3. In an apparatus for controlling the dispensing of a selected volumeof a fluid from a source of the fluid to points of distribution of thefluid, the combination comprising: reciprocating actuating meansincluding a driven rod; a transverse plate mounted on said driven rod; aplurality of cylinders each having an inlet communicating with saidsource and an outlet communicating with one of said points ofdistribution; plunger means movable in each cylinder between an openposition in which said inlet is open for the passage of fluidtherethrough and a closed position in which said plunger means obstructsthe passage between said inlet and outlet to halt the flow of fluid tosaid outlet; and piston means movable in each cylinder and operable onsaid plunger means to move the same, said piston means being adaptedwhen withdrawn to vacate a volume in a respective cylinder and therebycreate a partial vacuum after said plunger means obstructs said cylinderto draw fluid into said cylinder through said outlet; said cylindersbeing spaced equally about said driven rod, to have said piston rneansdisposed parallel with said driven rod, said piston means each having aportion which projects outwardly of its cylinder and which is attachedto said transverse plate whereby actuation of said actuating means aftersaid selected volume has been dispensed withdraws said piston means andmoves said plunger means to said closed positions.

4. An apparatus in accordance with claim 3 together 'with means forvarying the longitudinal position of each plunger means relative to itspiston means and means for varying the position of said plate on saiddriven rod for adjustment of the amount of said vacuum created.

-5. In an apparatus for controlling the dispensing of a selected volumeof a fluid from an input conduit connected to a source of the fluid toan output conduit connected to a point of distribution for the fluid,the combination comprising: a cylinder having an open inlet endcommunicating1with said input conduit, an outlet communicating with saidoutput conduit, a first passage connecting said inlet and said outlet,and a second passage communicating with said first passage beyond saidinlet and having a greater cross sectional area than said first passage;a guide slideably received within said second passage; a plungerconnected to said guide for concurrent movement and operable in saidfirst passage, said guide and said plunger being movable between an openposition in which said inlet is open for the passage of fluid throughsaid first passage to said outlet and a retracted position in which saidplunger moves into said first passage to obstruct the same and halt theflow of fluid to said outlet and in which said guide moves within saidsecond passage to create a partial vacuum that draws fluid from saidoutlet conduit to said cylinder; and actuating means adapted whenactuated to move said guide and said plunger to said retracted positionupon the completion of the dispensing of said selected volume of fluid.

6. In an apparatus for controlling the dispensing of a selected volumeof a fluid from an input conduit supplied with fluid under pressure froma source to a plurality of output conduits connected to points ofdistribution for the fluid, the combination comprising: a plurality ofcylinders each having an open bottom forming an inlet communicating withsaid input conduit, an outlet communicating with one of said outputconduits, a first passage connecting said inlet and said outlet, and asecond passage of greater cross sectional area than said first passageand being aligned with said first passage beyond said inlet; a guideslideably received within each of said second passages; a plunger rodextending from each guide through said first passage and having a crosssectional area less than that of said first passage; a plunger securedto the extending end of each plunger rod and of a cross sectional areasubstantially that of said first passage, said guide and said plungerhaving an open position in which said guide is bottomed in said secondpassage and said plunger is disposed within said input conduit for thepassage of fluid from said inlet to said outlet; and reciprocatingactuating means including a driven rod connected to said guides to movesaid guides when actuated to retract said plungers within said firstpassages to halt the flow of fluid through said first passages and tomove said guide within said second passages to create a partial vacuumto draw fluid from said output conduits into said cylinders.

7. In an apparatus for controlling the dispensing of a selected volumeof a fluidyfrom an input conduit connected to a source of the fluid toan output conduit connected to a point of distribution for the fluid,the combination comprising: a cylinder having an open inlet endcommunicating with said input conduit, an outlet communicating with saidoutput conduit, a first passage connecting said inlet and said outlet,and a second passage communicating with said first passage beyond saidinlet; a guide slideably received within said second passage; a plungerextending through said first passage and yieldably connected to saidguide, said plunger being movable between an open position in which saidinlet is open for the passage of fluid through said first passage tosaid outlet and a closed position in which said plunger seats againstsaid inlet to block the same; and actuating means operable on said guideand adapted when actuated to move said guide in said second passage tomove said plunger to said closed position and to thereafter continue tomove said guide within said second passage to create a partial vacuum,whereby fluid is drawn into said cylinder from said output conduit.

8. In an apparatus for controlling the dispensing of a selected volumeof a fluid from an input conduit supplied with fluid under pressure froma source to a plurality of output conduits connected to points ofdistribution for the fluid, the combination comprising: a plurality ofcylinders each having an open bottom forming an inlet communicating withsaid input conduit, an outlet communicating with one of said outputconduits, a first passage connecting said inlet and said outlet, and asecond passage communicating with said first passage beyond said inlet;a guide slideably received within each of said second passages; aplunger rod slideably received in a through bore in each of said guides,said plunger rod having an upper end which extends above said guide andalower end which extends through said first passage; a plunger securedto the lower end of each plunger rod of a cross sectional area greaterthan said inlet; a compression spring biased between the upper end ofeach guide and shoulder means on the upper extending end of said plungerrod, said guide and said plunger having an open position in which saidguide is bottomed in said second passage and said plunger is disposedwithin said input conduit for passage of fluid from said inlet to saidoutlet; and reciprocating actuating means including a driven rodconnected to said guides to lift said guides when actuated to retractsaid plungers to seat the same against said inlets and thereby halt theflow of fluid through said inlets and to thereafter continue to liftsaid guides against said springs to move said guides within said secondpassages to create a partial vacuum to draw fluid from said outputconduits into said cylinders.

References Cited by the Examiner UNITED STATES PATENTS 3/1926 Fenton222-380 2,839,226 6/1958 Ross 14lll7 X M. HENSON, WOOD, JR., PrimaryExaminer.

1. IN AN APPARATUS FOR CONTROLLING THE DISPENSING OF A SELECTED VOLUMEOF A FLUID FROM A SOURCE OF THE FLUID UNDER PRESSURE TO A POINT OFDISTRIBUTION OF THE FLUID, THE COMBINATION COMPRISING: A HOLLOW CYLINDERHAVING AN INLET COMMUNICATING WITH SAID SOURCE, AN OUTLET COMMUNICATINGWITH SAID POINT OF DISTRIBUTION, A FIRST PASSAGE CONNECTING SAID INLETAND SAID OUTLET, AND A SECOND PASSAGE COMMUNICATING WITH SAID FIRSTPASSAGE BEYOND SAID INLET AND OF A GREATER CROSS SECTION THAN SAID FIRSTPASSAGE; PLUNGER MEANS MOVABLE IN SAID FIRST PASSAGE BETWEEN AN OPENPOSITION IN WHICH SAID INLET IS OPEN FOR THE PASSAGE OF FLUIDTHERETHROUGH AND A CLOSED POSITION IN WHICH SAID PLUNGER MEANS OBSTRUCTSSAID FIRST PASSAGE TO HALT THE FLOW OF FLUID TO SAID OUTLET; PISTONMEANS MOVABLE IN SAID SECOND PASSAGE AND ADAPTED WHEN WITHDRAWN TOVACATE A VOLUME IN SAID CYLINDER GREATER THAN THAT DISPLACED BY MOVEMENTOF SAID PLUNGER MEANS TO SAID CLOSED POSITION WHEREBY A PARTIAL VACUUMIS CREATED TO DRAW FLUID INTO SAID CYLINDER THROUGH SAID OUTLET; ANDACTUATING MEANS ADAPTED WHEN ACTUATED TO MOVE SAID PLUNGER MEANS TO SAIDCLOSED POSITION AND TO WITHDRAW SAID PISTON MEANS, WHEREBY THEDISPENSING OF FLUID IN EXCESS OF SAID SELECTED VOLUME IS PREVENTED.